Wireless communications devices are an integral part of society and permeate daily life. The typical wireless communications device includes an antenna, and a transceiver coupled to the antenna. The transceiver and the antenna cooperate to transmit and receive communications signals. A typical RF transceiver includes a power amplifier for amplifying low power signals for transmission via the antenna.
One example of a wireless communications device is a high frequency (HF) wireless communications device. The typical HF wireless communications device covers the frequency range of 2-30 MHz and provides several benefits. For example, the HF wireless communications device offers potential worldwide communication capabilities with little to no infrastructure. Indeed, HF communication is popular with many amateur (HAM) radio operators, permitting one operator to readily contact another operator on another continent. The long range of HF wireless communication systems is the result of the desirable propagation characteristics of HF waves, resulting from their refraction by the Earth's ionosphere. However, long range HF communication can be affected by varying ionospheric conditions. Conditions that may affect HF communications include, for example, sunlight/darkness at site of transmission and reception, season, solar sunspot cycle, solar activity, and polar aurora. In particular, these conditions can cause only some HF frequencies to be usable on a particular link; which frequencies are usable at any given time may be difficult to predict. Accordingly, the user may be forced to manually cycle through several frequencies to find a channel suitable for transmission.
An approach to this drawback in HF communication systems is an automatic link establishment (ALE) method. The ALE method typically includes automated procedures for evaluating the propagation characteristics of multiple frequencies and selecting a suitable frequency on which to establish a link among two or more stations desiring to communicate. Helpfully, the user of the HF communication system need not manually scan and evaluate the available frequencies. When a communication is initiated, the transmitter device selects the best available frequency for the desired transmission path.
HF communication systems have typically utilized 3,000 Hertz (3 kHz) of bandwidth for a given channel. Several data signaling standards have been developed for these 3 kHz channels. These standards typically support up to 9,600 bits per second (bps) data communications over 3 kHz HF channel links. In addition, several ALE standards have been developed to support the 3 kHz bandwidth channel.
As the demand for higher data rates continues to grow, new waveforms/standards are being developed, which expand the utilized bandwidth from 3 kHz up to 24 kHz in 3 kHz increments, and the data rate capability from 9,600 bps to 76,800 bps for HF skywave links and 120,000 bps for benign HF surface wave and skywave links. These HF waveforms are referred to as wideband HF waveforms.
Notwithstanding the benefits of the wideband HF wireless communications device, the typical user of such HF wireless communications devices may experience difficulty in establishing a communications link due to propagation and interference. In particular, if the wideband spectrum assigned to a user includes a number of interferers, the user may spend a significant amount of time to determine the usable parts of the wideband spectrum.
One approach to frequency selection is disclosed in U.S. Pat. No. 5,734,963 to Fitzgerald et al. This narrowband, i.e. a typical 3 kHz bandwidth, HF approach includes an HF communication system comprising a plurality of radio base stations (RBSs) and field units. The field units use detected noise levels, detected interferers, and known fixed transmitters to determine the appropriate frequency for transmission. The RBSs maintain databases for the frequency spectrum, which include received signal strength characteristics.